11/11/2024
Introduction t Hydrogets
in conservatio
Restauratoren Nederland CollectieCentrum Nederland
Instructor: Matt Cushman 18-22 November 2024
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Workshop Outline	INTRODUCTII RN  I COLLEC
Day 1:18 November 2024	D N TO h TIECENT
• Introductions	YDRO RUM [
• Lecture Part I: Key Concepts	GELS JEDER
• Why gels?	> z z o a O
• Control, developing a range of cleaning "tools"	— z _^ <s> co rn ' 70
• Some loose definitions	ro >
• Relating polymer structure and network structure to gel	° O ''• Z ^ o
properties	.EANI 3ER 2
• Mass transfer in gel cleaning	o z O
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Workshop Outline	INTRODUCTII R N  I COLLEC
Day 1:18 November 2024	DN TO N T I E C E N T
• Lecture Part II: Practicalities of Formulation and Use	73 -< a o m TO
• Mixing methods	OGELS
• Heating/cooking options	> Z z o
• Casting tips	a q — z _^ u> co rn
• Application methods	^ >
• Storage tips	z ^ o
• Preservative options	.E ANI NG 3ER 2024
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Workshop Outline	INTRODUCTII RN  I COLLEC
Day 1:18 November 2024	IN TO h Tl ECEN1
• Lecture Part Ilia: "Rigid Gels"	YDRO RUM I
• Agar & agarose	GELS JEDE
• Gellan gum	z ^ o
• Sidebar: alginate gels	0 NS E RVATI 0 M CLE! ) I  18-22 NOVEMBE
	7J >-Z z ^ a o
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Workshop Outline	INTRODUCTII R N  I COLLEC
Day 1:18 November 2024	ONTO ^ T I E C E N 1
• Lecture Part IV: "New" Gel Materials	YDRO RUM
• Polyvinyl alcohol)-borax gels	°" S t"
• Nanorestore Gels: Dry & Peggy	> Z z o
• Xanthan-konjac/agar(ose) double-network gels	a o — z _^ u> co rn
• Curdlan	RVATION C -2 2 N 0 V E IV
• Q&A	LEANING IBER 2024
• End of day: 5:00	
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Workshop Outline	INTRODUCTII RN  | COLLEC
Day 2 - Practical: 19 & 21 November 2024	D N TO N T I EC E N T
• Gel preparation demonstrations	YDROi RUM N
• Comparative moisture delivery experimentation	1X1 m □ 73
• Delivery techniques	W CONS E RVATI0N C L1 .AND |  18-22 NOVEMB
	£ > z o z ^ a O
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Workshop Outline	INTRODUCTII R N  | COLLEC
Day 3 - Practical: 20 & 22 November 2024	3 N T 0 H T I E C E N T
• Incorporating aqueous chemistry	YDROI RUM N
• Incorporating solvents	3ELS 1 E D E R 1
• Experimenting & problem solving on test surfaces	z ^ o a o — z _ (ft CO fTl
• Wrap-up discussion	RVATION CLEANIN -2 2 NOVEMBER 20;
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Course Coals
1. Consider alternative modes of delivery for and cleaning (and humidification)
2. Develop a sense for identifying useful gel properties
3. Describe methods of formulating and manipulating hydrogels to match desired effects
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Cleaning: It's All About Control
"Control. Control. You must learn control."
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33 — z Z The Nature of Aqueous Solutions	
Properties to tailor •pH	— z I Additional factors: y 1                     z °
•Conductivity •Use of chelating agents	. Time           t. °i= . Mechanical action ?» solvents ~5
•Use of surfactants	ATION C 2 N 0 V E M
•Viscosity/rheological agents -	LEANING 3 E R 202 (1)
• Reactive additives: enzymes, redox reagents ©	
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^ Z — 73
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AQUEOUS KEY CONCEPTS:
• As pH increases, acid groups become deprotonatea (charged)
• If pKa is known, uie can predict the pH when the acid group becomes deprotonated (charged)
• Greater charge: increased solubility in water (generally)
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AQUEOUS KEY CONCEPTS:
• We can control the pH of solutions with the addition or a buffer
• We only need a few buffers to couer the range of our typical work
• We influence what is retained and what is remoued by controlling pH
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AQUEOUS KEY CONCEPTS:
• We influence swelling on manu surfaces by adjusting conductiuity
• With pH, conductiuity has a large influence on what is retained
• An isotonic solution will limit swellings key for retention of originalmaterials
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Many of our cleaning challenges can be solued by controlling pH and conductiuity and by selecting an appropriate chelating agent
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Why Cels? Practical Considerations
• Handling Properties: Control!
• Health & Environmental Safety
• Economic Considerations
• Compatibility with Other Aqueous Solution Parameters!
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Some Loose Definitions
— Z
Thickener /Thickening Agent 1°
A hydrophilic, relatively high-molecular-weight if
material added to a solution to increase viscosity l\
with little influence on the structure or fluid dynamics
of the solution 11
_^ in
Spreadable Gel 1
A solution with a concentration of thickening agent:
• having a semi-solid, weakly cohesive structure
• having varied response to applied shear ^
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Spreadable Cels: Benefits
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Inexpensive; easy formulation
Cellulose ethers, xanthan gum, Pemulen TR-2
Polymer-stabilized emulsions
Add up to 30% (v/v) non-water-miscible solvent
Aliphatic/aromatic:
mineral spirits - xylenes (e.g.)
Aliphatic/aromatic alcohols: butanol - benzyl alcohol
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Some Loose Definitions
23
— Z
Hydrogel 1°
A hydrophilic, three-dimensional network of if entangled and/or cross-linked polymeric material |? containing >~90% water. ll
21 o a O — z _^ tn co m
Despite its high water content, the hydrogel is not ll soluble in water! <s
m <">
m rn
73 > Z
o z
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Useful Propertie	s to Exploit	INTRODUCTIO R N  | C 0 LL EC1
• Gel cohesion		H TO H ' 1 E C E N T
• Elasticity/Rigidity	• Solvent compatibility	YDROGELS II RUM NEDERL
• Water retention	• Optical properties	z o a o — z _^ u> co rn
• Thermo-reversibility/ Heat stability	• Ease of formulation	z ^ o m m 73 > ° z ^ CI O
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Factors Determining Gel Properties B Rheology
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Thickener/gel molecular weight & concentration
Polymer/oligomer structure
• Straight vs. branched
• Regularity/homogeneity of repeat units
• Degree of substitution: frequency of side chains
• Hydrophilic & hydrophobic substructures
• If hydrophilic: Ionic? Hydrogen bonding?
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Factors Determining Gel Physical Properties
Type(s) of polymer chain junctions
* Chain entanglement & transitory interactions (physical gels)
* Covalent cross-linking (chemical gels)
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Chemical Crosslinking facilitated by:
• Crosslinking agents
• Polymer-polymer crosslinking
• Photosensitive agents
• Enzymatic crosslinking
Physical Crosslinking facilitated by:
• Hydrophobic interactions
• Ionic interactions
• Hydrogen bonding
• Chain entanglement
• Crystalline formations
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Factors Determining Cel Properties	1 N T ROD RN  1 CC
B Rheology	UCTION T LLECTIEC
• Solution parameters ("solvent quality")	0 HYD E N T R L
• pH - gel stability; ionization state of acid groups	ROGE VI N E
• Ionic environment (conductivity, e.g.)	L S 1 0 E RL
• Presence of divalent metal ions (Ca2+, e.g.) - ionic crosslinking	z ^ o a o
• Co-solvents' concentration and solubility parameters	NSERV 18-2;
• Processing	ATION C I NOVEfc
• Physical mixing	m m 3J >
• Crosslinking (chemical gels)	11 N G 2 0 2 4
• Temperature processing	o
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Cel Polymers	INTRODUCTIC R N  1 C 0 LL EC
• Natural polymers	)N TO T 1 E C E N
• Proteins	—i re 73 -< cz a
• Polysaccharides	ROGE VI N E 1
Simple preparation	73 > z
• Synthetic polymers	: 0 N SE R d i 18-;
• In theory: great variety of options	^ >
• In practice: additional processing requirements	° o ^ <■>
• Increased possibilities for crosslinking (chemical gels)	LEANING 3ER 2024
	©
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Polysaccharides	INTRODUCTIC RN  1 COLLEC
• Monomers: monosaccharides	— z Es
• Generally: 6- or 5-membered carbohydrate rings	—i re 73 -< cz a
• Stereochemistry contributes to polymer chain structure	o □ m
• Some monosaccharides are ionic	1X1 u> 73 > Z
• Glycosidic bonds	a O — z _^ <s> co rn
• Ether linkages created during condensation/dehydration reaction	^ >
between two monosaccharides	m Z
• Nomenclature: (n.,—>n2) describes the positions of the carbons	; L E iA Vi B E F
on the two monosaccharides	z o z
• a or ß describe the stereochemistry on either side of the bond	O
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Polysaccharide Structures				INTRODUCTIO R N  I COLLECT
HO ^O^SÄ1 HO H0^0%A1H0 C	HO HO-^HO^	y n	OH 6 / OH        4 <( OH	N TO    HYDROGELS IN CONSERVA' ECENTRUM NEDERLAND | 18-22 \
Amylose: (1—>4)-a-D-glucose			Cellulose: (1^>4)-ß-D-glucose	[ION CLEANING NOVEMBER 2024
				©
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Polysaccharide Chain Structures
^3
— Z
Fig. 1.1 Examples of molecular chain structure of polysaccharides
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Polysaccharide Selection	INTRODUCTIC R N  1 C 0 LL EC
• Rigid, brittle gels:	— z Z°
• More homogenous (esp. homopolymers)	—1 I 73 -< a o
• More crystalline in behavior (linear, rod-like structures)	o m °
• Fewer side chains, less branching	D E RL
• Increased junction density (crosslinking, chain entanglement)	> z z o a o — z
• Flexible, elastic gels:	E RVATI 18-22 N■
• Heteropolymers and branched polymers	o ''• z ^ <■>
• Polymer networks capable of significant swelling	B E R
• High density of strong and weak chain-chain interactions	II NG 2 0 2 4
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Biopolymer Thickeners 8 Celling Agents		INTRODUCTI RN  1 COLLEI
• Microbial • Gellan • Xanthan • Curdlan	• Animal	— z Es
	• Chitin/chitosan	HYDROGE TRUM NEC
• Seaweed & Algae • Agar • Alginate • Carrageenan • Vegetable • Guar gum • Gum Arabic • Konjac • Locust bean gum • Pectins • Tara gum	• Proteins • Case in ate • Gelatin • Soy protein • Whey protein	_S IN CONSERVATION CLEANING gk ERLAND |  18-22 NOVEMBER 2 0 2 4 W
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A Note on Natural Materials
For many natural materials, the source organism, geographical source and subsequent processing influence the quality of the raw material:
• Optical properties
• Odor
• Gel strength (MW)
It is best to prepare a test batch of gel when switching products!
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A Note on Food-Grade Hydrocollold Materials
CAUTION!
Some suppliers of food grade gelling agents and thickeners will include calcium or iron in their product. This increases ionic cross-Unking between chains with ionic substitutions.
For lesser-absorbent structures, this is probably fine. But such formulations are not recommended for paper supports, unprimed cotton or linen, or other substrates that could be degraded by metal-catalyzed hydrolysis reactions.
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Effect of Processing
By adding enough energy to the system, we p
allow polymer chains to fully hydrate and exist u
as random coils in solution. U
m w 73 — > z
Random coils then self-arrange to =| concentrate hydrophobic interactions (CH2 p backbone) and hydrophilic interactions U (hydrogen bonding, coordinated water, ions) if to form a somewhat regular structure
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Factors Determining Gel Physical Properties ✓ —11	
	S                                                                                                                                                                                                                                                                73 -< _, o Polymer type, concentration, 5™ ^\             cross-link/entanglement density,                 ? = \^          and solvent quality °° \ w I                                                                                                                                                                                    co rn
	determines mesh size or "pore size" ~> {•fc                                                                                                                                                                                                                                          ° Ö z /         ^\                                                                                                                     s ° [                            ^\                                                                                                                                                                                              m m \                                        \ 7J> \      \                                                              1                                                                                                                                                                                                                                                                                                                                                  NJ Z
	\           y                                                                         °z \ ©
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Concentration Considerations
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• With increasing concentration: • Decreased mean pore size
2% Agarose
At
1 pm
6% Agarose
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/on/c Crossllnktng
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• Electronegative groups can coordinate with divalent ions
• Method for linking between polymer chains
Food HydrocoUaids 118 (2021) 106782
Alginate gel
Fig. 2. Alginate gel structure in presence of calcium ions (egg-box model) (Adapted from Martau el bl, 2014).
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Diffusion In Hydrogels
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Solutes will diffuse through hydrogels if:
• It would normally diffuse freely in a solution of the same composition
• The solute is smaller than the mesh/pore size of the hydrogel
Diffusion will be inhibited if:
• The solute encounters an energetically favorable location
• The average mesh size < solute size
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Capillary Action In Hydrogels
• In simplistic terms:
• Capillary action is driven by surface forces between the gel material and the liquid phase
• Capillary action is spontaneous and occurs without the application of external pressure
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A simple model of capillary action in hydrogels: a bundle of tubes with a uniform radius
In a hydrophilic, porous medium, it is expected that capillary forces will imbibe water into the structure.
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Synerests	INTRODUCTII RN  | COLLEC
• With applied stress, and relaxation of stress, the	)N TO T 1 E C E
microstructure of the gel can be altered:	H Y D M T R U
• Helical structures can tighten	o ^ a
• Physical bonds can break and reform	ELS 1 D E R
• The gel structure can become more dense	z ^ o a o
• and water can be expelled spontaneously: syneresis!	NSERVAT 18-22 N
• Syneresis can be caused by slight temperature changes, gel	ION CLE OVEMBE
"maturation", introduction of differing solvent quality	ANING R 2 0 2 4
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73 —
Moisture Delivery and Retention
Syneresis       Capillary Action
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GEL RHEOLOCY 8 MOISTURE RETENTION
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General Trends: Rheology and Moisture Retention
With decreasing pore size:
• Decreased rates of diffusion
• Increased capillary action
Increased polymer concentration and junction density will increase moisture retention
With increasing brittleness: • Increased syneresis
Flexible, elastic gels will exhibit decreased syneresis
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General Concepts: Hydrogels
• Think of hydrogels as a "vessel" for delivering water/moisture
• Lower polymer concentration: more open structure; vessel empties faster
• Better surface contact: more efficient diffusion and capillary action
Smaller mesh/pore size: increased capillary action, but slower delivery. Testing will help you to find the balance!
Intentional Formulations
Intentional polymer selection, concentration, appropriate thermal processing, solution formulation
will result in gels that:
• are brittle, tough, elastic, stiff, loose, cohesive, fluid
• control delivery of aqueous chemistry
• provide beneficial working properties for the conservator
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Mass Transfer in Cel Cleaning
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Gel matrix
Free Water
Solutes
Can we formulate and load a gel to control how material moves into and away from the surface?
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Mass Transfer: Practicalities	INTRODUCTI R N  1 C 0 LL E(
• Predicting mass transfer can be difficult:	ONTO DT 1 E C E
• Heterogeneous gel pore/mesh size	HYDRI ^ T R U M
• Gel surfaces often have small flaws	IGELS IN M E D E RL,
• Surface contact can be incomplete	CONSEF \ N D 1 18
• Unpredictable interactions between solutes & gel matrix	IVATION 2 2 N OV E
• Unpredictable influence of object porosity, condition, treatment	CLEAN VI B E R
history etc. etc. etc.	1 NG 2 0 2 4
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73 ~ Mass Transfer: Practicalities o —		
		• Questions to ask: :> • >4re we able to control the delivery of =L moisture? =° ^ *j o m m • Is the solution achieving the desired result? ™» > z 21 o • Is the time scale appropriate? -|
		• Are solubilized/affected materials sorbed ~s into/onto the gel, or do they remain at the         < s surface of the object? 1? S >
		• Once cleaning is complete, are there signs of ~* residues from the gel matrix and/or the delivered solution? O
		
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PART II:
HYDROCEL PREPARATION FOR CONSERVATORS
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Useful Equipment
• Scale
• Ideally: accuracy better than 0.05g (kitchen scales < USD 20.00)
• Mixers
• Magnetic stir plates (some compact units < USD 40.00)
• Battery-powered milk frothers/mixers (USD 6.00-20.00)
• Stir rods, spatulas
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Mixing Tips	INTRODUCTIO R N  | C 0 LL EC!
• Overnight hydration	— z
• Good idea for high-viscosity solutions	YDROGE RUM N E [
• "Pre-Hy"	LS IN CO ) E RLA N D
• Use an immersion/stick blender to quickly disperse	— z _ (ft CO fTl
polymer and eliminate "fisheyes"	^ >
• Creates SO MANY BUBBLES	o 3 ^ Z s o
• Vibration stage	LEAN B E R
• Vacuum pump	2 0 2 4
• Generally not going to be a problem with vigorous heating	o
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Useful Equipment		INTRODUCTIO RN  | COLLEC"
— z • Hot plate Is —i re • For water baths (search for home brewery equipment) 1° o m m		
• Immersion circulator \ • For precision temperature contrc (some models USD 60.00)		L S IN CO NS E RVATI 0 N IERLAND |  18-22 NOV
• Microwave		CLEANING EMBER 2024
	*	
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Microwave Method
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Disperse polymer in distilled water in a microwave-safe container. Cover loosely!
Microwave on half power for 20-30s at a time
Remove from microwave and swirl after each heating
Avoid allowing the solution to boil over!
nttps://www.youtube.com/watch?v=V490Ku FsU4k
As solution cools, but before gelation, pour into mold
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Immersion Circulator Method
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• Set bath temperature above the hydration/melting temperature
• Disperse polymer in distilled water (or other solution) in a well-sealed container or bag
• Submerge container in bath; remove periodically to mix contents
• Allow the contents to reach the bath temperature; remove from bath
• As solution cools, but before gelation, pour into mold
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Immersion Circulator Method
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Tip: Rare earth magnets can be used to keep enclosed solutions submerged.
Pictured:
silicone-coated magnets for sous-vide cooking outside the bath and a small rare earth magnet inside the jar.
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Caution!
Take extra caution when handling hot solutions!
Hot, viscous gel solutions will stick to your skin, making burns worse!
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Useful Equipment - Molds
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Silicone molds -food prep, baking, candy making
Glass containers - Petri dishes, watchglasses, ashtrays
Pyrex dishes
Mylar/ Melinex trays
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Useful Equipment - Molds
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Tip: Silicone splicing tape!
• Adheres to silicone molds — labeling
• High temperature tolerance
• Easily removable
• Can be reused: securing small rolls of Mylar scraps
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			7J ~ ...... Z —
Measuring pH ofCels	66W		ODUCTION TO COLLECT ECE
• Use enclosed, all-in-one electrodes			HYDRC M T R U M
• Spear probe meant for soft foods; flat			IGELS 1 M E D E RL
surface probes		i	= o
• pH indicator papers or test strips		pMTr	IRVATION CLE 3-22 NOVEMBE
We can measure gel conductivity using a flat conductivity		t	ANING R 2 0 2 4
meter like the Horiba Laquatwin EC meter!		—i	e
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Storage: Limiting Handling and Oxygen Exposure
• High moisture content and polymer composition present favorable environments for biological activity
• Use clean glassware and molds; sterilize tools
• Wear gloves when handling
• Store between Mylar/Melinexfilms in the refrigerator
Star-like growths in a gellan hydrogel
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Storage: Limiting Handling and Oxygen Exposure ■
• Storage in aqueous solution
• Storage in hydro-alcoholic solutions
Vacuum sealing
• Silica gels
• Oxygen scavengers
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Potentially Useful Equipment: Vacuum Sealers
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Considering Preservatives	INTRODUCTIO R N  | C 0 LL EC"
• Preservatives can prolong the usable life of a hydrogel	1 TO 1 " 1 E C E N
preparation	HYDROG F RU M N E
• However:	E LS 1 N D E RLA1
• Health and safety concerns (esp. parabens)	^ o a o — z _ tn
• Preservatives may contribute unwanted solubility parameters	CO fTl 73
• Some preservatives are fatty acid salts - could contribute to	^ >
metal soap formation	N CLEANING /EMBER 2 0 2 4
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Selected Preservatives
• Parabens (Germaben II) - Not recommended!
• Phenoxyethanol-0.5%; Permissible <1% w/v
Can decarboxylate with heat: benzene...
• Potassium sorbate - 0.025%; requires acidic pH
• Sodium benzoate - 0.05%; requires acidic pH
Preservatives might be best used for test kits meant to be kept at room temperature - not for full treatments.
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Preservative for Nontontc Gels:		7J — ...... Z — o o
e-Poly-l-lyslne (e-PL)	n	JUCTION TO 3 LL ECTIE C E
• GRAS; biodegradable h-	I ii	HYDROI : N T R U M K o
• High solubility in water	I ii h O	°™ m w n                      > z
• Stable in a wide pH range, 2-9.5	n =	25-35 — z _^ u>
• Effective against a broad range of pathogens		co rn ^ >
• High MW (unlikely to migrate into surfaces)		10 N C L 0 V E M B
• Effective at 0.025% w/w		E A N 1 N ( ER 2 0 2
* May contribute turbidity with anionic biopolymers		
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73 — ^ Z
— 70
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— z
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1 TO
TYPICAL APPLICATIONS 8 DELIVERY METHODS
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Cold Methods	73 — z Z Warm Methods 23
• Use of cast gels:	— Z • Use of warm solutions: -73 -<
• Surface testing	• ln-situ casting |i
• Controlled moisture delivery	• Syringe, brush application — z
• Stain reduction/poulticing	co rn • Embedded fabric supports <°
• Surface cleaning	• Sprayed application % r-o Z ° Z ^ a O
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73 — — 73
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PART lilt "RIGID" GELS
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Agar - Industrial Production
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Agar is a biopolymer contained within cell walls of red algae
Major component: agarose
OH OH
--O
OH
HO
"OH
• Fraction inhibiting gelling: agaropectin(s), a complex mixture of carbohydrates and sulfates thereof
Cold waters —> thicker cell walls (more to extract)
Geographical location, environmental factors contribute to product quality
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7J — z z Usable Agar Products 23			
— Z • Food-grade agar - -10-30 USD/1 OOg ¥ 7J ■<			
• Technical agars (bacteriological) - -		-30 USD/1 OOg |l 73 > Z	
	agar agar § powder		DO NS E RVATI 0 N CLEANING ID |  18-22 NOVEMBER 2024
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4 Note on Food-Grade Hydrocollotd Materials
CAUTION!
Some suppliers of food grade gelling agents and thickeners will include calcium or iron in their product. This increases ionic cross-linking between chains with ionic substitutions.
For lesser-absorbent structures, this is probably fine. But such formulations are not recommended for paper supports, unprimed cotton or linen, or other substrates that could be degraded by metal-catalyzed hydrolysis reactions.
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Agarose Purification
Agaropectin(s) removed from high quality agar: • Various processes: precipitation, extraction, absorption
Processing methods contribute to product quality! Additional processing adds to expense: >100 USD/1 OOg
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Agar 8 Agarose Properties
to Consider: Gelation Hysteresis
sol state
initial gel
final gel structure
Reversible process: sol - incipient gel - elastic gel* -turbid rigid gel - expression of water (syneresis!)
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Agar 8 Agarose Properties to Consider
• Optical properties: color, transparency
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Melting temperature
Gelation hysteresis!
Gelling temperature
Gel strength
Sulfate %
Homogeneity/purity/ionic quality
EEO (electroendosmosis)
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Agar or Agarose? Which Type?
• What is the goal of the treatment step?
• Simple hydration/humidification: Agar ($)
• Increased gel flexibility: Agar
• Large surface areas: Agar ($)
• Controlled hydration/humidification: Agarose
• Controlled delivery of aqueous cleaning solutions: Agarose
• Aqueous cleaning on water-sensitive surfaces: Agarose
• Controlled delivery of temperature-sensitive reagents: Low-gelation-temperature agarose (Very expensive!)
Preferred agarose: Agarose LE (low electroendosmosis).
Concentration Considerations
• With increasing agar/ose concentration:
• Decreased mean pore size h
O
2% Agarose 6% Agarose o
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Concentration Considerations
Typical concentrations range from -1% -10+% (w/v)
With increasing agar/ose concentration:
• Increased water retention
• Increased gelation temperature (lesser gelation hysteresis)
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Agarose Moisture Delivery/Retention
Greater gel concentration :: greater retention 'Fresh' gels :: lesser retention
"E
1 % Agarose 2% Agarose 4% Agarose 5% Agarose B% Agarose 10% Agarose
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A Thought Experiment
2;
• Agarose gel of lower concentration %
C
21 c 1X1 r
• Relatively flat, thin object with stains
° C _^ c
• Agarose gel of higher concentration ■
s < m r
=° ?
In what direction should the water and stains move?
c
Adding Aqueous Cleaning "Tools"
e< e<
• Agarose most stable in pH ranges 5-9 ^
1= c
m ' c c
• Two options for tailoring aqueous parameters:
• Add to agarose solution before heating
• Allow cast gel block to equilibrate in aqueous solution =j
• Components to avoid heating: enzymes, surfactants %
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— 73
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AGAR 8 AGAROSE IN CONSERVATION: Applications
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Agar S Agarose - Cofd Methods	INTRODUCTION R N  1 COLLECT
• Use of cast agarose: • Surface testing	1 TO HYDROGEL ECENTRUM NED
• Controlled moisture delivery	S IN CON ERLAND
• Stain reduction/poulticing	SERVATIOI* 18-22 NOV
• Surface cleaning	1 C LEANI NG A EMBER 2024 IP
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Estimating Surface pH and Conductivity
Erica Rota, Claudio Bozzi, Paolo Cremonesi & Anna Lucchini (2021) Study of the Best Methodology for Measuring Surface pH of Linen Canvas, Studies in Conservation, 66:6, 313-320, DOI: 10.1080/00393630.2020.1838711
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Large-Scale Stain Reduction
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"Stain Stick"
4. CAST THE GEL
While the gel is still hot and liquid, pour it carefully into the cut open end of the syringe. Standing the syringe on the end of the plunger is usually stable - if it is not, have a partner hold it for you. Pour excess gel into other prepared syringes or into a flat, heat-proof container for use as a cast gel. The syringes take longer to set than cast gels because they retain heat longer in their cylindrical shape! Leave the gel for at least thirty minutes to ensure it is fully set. The agarose will appear slightly hazy and blue when set.
5. USE THE GEL
Push the plunger down slightly to expose the gel. With a dean blade, cut the gel flush with the plastic syringe to trim off the meniscus of the gel. The "Stain Stick" is now ready to use! Lightly pounce on your object where necessary; longer dwell time or more pressure will release more water. Try cutting the tip of the gel into a chisel or point for detailed work! Avoid vigorous rubbing across the object's surface, which can cause crumbling of the gel and abrasion of the object's surface. As the end of the gel becomes stained with imbibed discoloration products, trim it off with a clean blade. Store the gel in a plastic bag and in the refrigerator for up to two or three weeks.
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SYRINGE-CAST AGAROSE HANDOUT, M. BROCKMAN, ED. 2020 2
Image: Madison Brockman, AIC BPG
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Surface Cleaning: Crated Crumbs
73 > ° Z
Paolo Cremonesi (2016) Surface cleaning? Yes, freshly grated Agar gel, please, Studies in Conservation, 61:6, 362-367, DOI: 10.1179/2047058415Y.0000000026
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		n to hydro! FIECENTRUM K
»                                       ^£---.1.	\, \p	sels in conservation cleaning EDERLAND |  18-22 NOVEMBER 2 0 2 4
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Warm Application/ln-situ Casting
Concerns:
• Temperature stability of original surface
• Ingress of fluid solution into cracks and pores
• Personal safety: Hot gel and exposed skin are a bad mix!
But consider:
• If the gel temperature is sufficiently low, you can wait to apply the warm solution to the surface just before gelation
• If the gel concentration is high, you can expect faster gelation, limiting ingress
• Temporary hydrophobization may protect cracks and pores
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Agarose - Warm Brush/ Poured Application
Agarose - Warm Brush/ Poured Application
^ Gl
Diana Hartman, Laura Eva Hartman & Caroline Hoover (2019)
Experimenting with Agarose: New Methods for Cleaning Sensitive
Modern and Contemporary Surfaces, AIC Paintings Specialty
Group Postprints 32, 157-172. ©
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Agarose - Warm Brush/ Poured Application
in
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Agarose - Warm Application
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Agar - Sprayed Application
o °
Ambra Giordano & Paolo Cremonesi (2021) New Methods of Applying Rigid Agar Gels: From Tiny to Large-scale Surface Areas, Studies in Conservation, 66:8, 437-448, DOI: 10.1080/00393630.2020.1848272
113
Surface Conformation
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CELLAN CUM
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Cellan Cum
0 H      >—0 H
......
OH  HO      OH  HO      OH   HO OH
Bacterial branched anionic gum      g|ucose g|ucuronlc g|ucose rhamose
acid
•Backbone of glucose, rhamnose, glucuronic acid
•Occasional acetyl (<50% of tetrasaccharides) and glycerol (>50% of tetrasaccharides) substitutions
Practical Considerations
•Fairly expensive (USD 40.00/1 OOg) •Hydrates in cold water
•Typical concentrations: 0.75-2.0%; can be greater
•Creates very viscous solutions
•Heated solutions are very clear, less viscous
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Cellan Cum - Acyl Substitutions
Natural form: High-acyl gellan gum
•High numbers of acyl groups: flexibility, opacity
Low-acyl gellan gum
• Chemically treated to remove most acyl groups
• Fewer substitutions: more rigid structure
• Optically less cloudy than agar gels
Both structures require calcium ions to stabilize the gel: 0.4g Calcium acetate added per 1L
117
Cellan Cum Preparation	INTRODUCTIC R N  1 C 0 LL EC
Material selection decisions	INTO T 1 E C E N
•High-acyl: less common in conservation applications	H Y D R TRUM
•Low-acyl: more common; used similarly to agar/ose	o a °"
•Two main suppliers: CP Kelco, Royal DSM	m yj 73 > z
•Polymer concentration	21 o a o — z _^ u>
General procedure	: RVATIO 3-22 N 0 \
•Dissolve calcium acetate in water	■ Z
•Add gellan gradually, with mixing	m m 73 >
•Heat to clarity (near boiling)	° z ^ a
•Cast into prepared mold/form	o
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Cetlan Hydrogels: Notes
Gellan mixtures can form clumps. If time allows, allow the mixture to sit overnight to promote hydration.
Gellan mixtures are often used as replacements for agarose (lesser cost!) but they do not exhibit the same syneresis
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Gellan Hydrogels: Notes
me.
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Tip: Use an immersion blender to rapidly mix and hydrate gellan (low-acyl or high-acyl)!
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Cetlan Cum - Effect ofCa2*
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0.4g Calcium acetate/1 OOOmL solution: ~2.5 mM
• Molarity: [(158.166 g/mol)(1 L/0.4g)]"1
(a)
4 mM
mM
(c)
20 mM
60 mM
TO
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We might be able to influence capillary action by adjusting Ca2+ concentration
121
Cellan Cum - Effect ofCa2*
Table 1
Water holding capacity W/Wu (%) of 1% gellan gels after 125 days storage at4°C
Ca++ (mM)	Average	Standard deviation
2	98.72	0.30
4	98.94	0.02
6	99.10	0.35
8	98.73	0.37
14	99.20	0.05
20	98.91	0.12
30	99.20	0.15
40	99.23	0.13
50	98.34	0.34
60	98.95	0.11
70	99.15	0.06
80	98.95	0.37
Water holding capacity appears to be independent of Ca2+ concentration
Syneresis is a minimal factor in low-acyl gellan gum moisture delivery
R. Mao et al. / Carbohydrate Polymers 46 (2001) 365-371
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Cetlan Hydrogets: Typical Applications
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Fig. 17 (liacnmo Lauro, I' i alii I S IVln in Vamano (lfi2(>), burin engraving. (A) before eleainne. ami (< :) alter treatment; (It) tin- rlearly yellowed gel alter treatment; (P) icheme of the applleation of the gel on a burin engraving
- T.innni-rt'lli .mil Sisr^iu   II!-; '/rj'ij.V.'jr-irrv i:! It 'ut> u|.H Jt uj R;;>rj- iriJf       ,' ( ^fi.rr { ;vi.
The Book and Paper Group Annual 29 (2010)
123
Cellan Hydrogets: Typical Applications
Fig. 14. Henry John White (Printer), The Holy Bible, (King James Version), 1832 or 1833, 28.0 x 22.0 x 6.0 cm, Library and Archives Canada, AMICUS 23024642.
Maheux Cross-Disciplinary Uses for Gellan Gum in Conservation   The Book and Paper Group Annual 34 (2015)
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Combing ing low-acyl and high-acyl gellan: Increased Flexibility
• Prepared in the same methods as agar/ose, creating a gel with interesting elasticity and efficient moisture delivery:
2% 9:1 low-acyl gellan gum:high-acyl gellan gum
Microwave method works well.
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Combining low-acyl and high-acyl jellan: Increased flexibility
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Comparing loiv-acyl, htgh-acyl, and blended gellan gum
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Re-using Thermoreuerstble Cels
• Collect like scraps and "clean" waste to re-melt
• Add water, fragment, re-heat, re-cast
• Concentration will be uncertain
• Perfect for non-presentation surfaces and "dirty" work
• Consider the addition of a preservative
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Particularly useful for expensive hydrogels like agarose.
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PART IV:
•NEW HYDROCELS
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PVOH-Borax Gels
Viscoelastic chemical gels
• Weakly coordinated bonds
• Highly viscous behavior
• Ductile
• Cohesive
• Self-healing behavior
• Good solvent compatibility
• Literature: minimal residues
• Poor pH stability (must be near neutral!) i\
• Properties can be tailored with component concentrations
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PVOH-Borax Cels: Components				INTRODUCTION RN  I COLLECT
	-		Na2B4Or 10H2O	TO HYDROG ECENTRUM NI
	HO_	n	H —0        0 —H \ / B / \ H —0       0 —H Potential Hazard!	ELS IN CONSERVATION CLEANING A EDERLAND |  18-22 NOVEMBER 2 0 2 4 V I
131
PVOH-Borax Cels: Complexatton
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Bonds within the complex are weak, transitory arrangements!
This means that the bonds can slip and re-form, allowing the gel to:
• mold to surfaces
• stretch under low stress
• break at high stress
• remain cohesive
• self-heal
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PVOH-Borax Cels: Preparation
Solution 1: PVOH, > 8%
Boraxsoiution      . Heat gently, with mixing, until clear
Spatula .  Qq not bQJI
• Allow the solution to cool
Disposable cup
Polyvinyl alcohol Solution 2: Borax, 8%
solution
• Heat gently, with mixing, until clear
• Do not boil
Add warm Solution 2 to cool Solution 1. Mix vigorously!
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PVOH-Borax Cels: Preparation
Gel properties determined by:
• PVOH molecular weight
• PVOH concentration
• PVOH/Borax ratio
A good starting point: 4:1 (w/w) 8% PVOH: 8% Borax
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PVOH-Borax Cels: Useful Solvents
Solvents can be added to PVOH solution prior to mixing
• Ethanol
• Isopropanol
• Methyl ethyl ketone
• Immiscible solvents (benzyl alcohol, e.g.) can be stabilized with a surfactant
Additions of 20-30% (v/v) possible Surfactant additions: 1-2%
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PVOH-Borax Gels: Solvent Effects
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, Valencia 2023
Developing conservation practices for cleaning gilded surfaces: Applications for xPVOH-borax organogels to clean two gilded frames
Variables:
• PVOH MW
• PVOH Wt%
• Borax Wt%
• Gel age
• Solvent(s)
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Keywords porirtwtyl *cohol)-borai. dsparson»(HVPO). gidtd obfSCts. frames
INTRODUCTION
Interest in high-viscosity polymeric dispersions (HVPDs) of partially hydrolysed polytvinyl alcohol) borax (xPVOH-b) for cleaning cultural materialsK arn.Mli et al 2009. Angelovarial 2011,2015. 2016. 2017.and 2018. Angelova 2013. Ricdo el al 2015 and 2017. Duncan 2017. Al-Emam et at 2019 and 2020. Al-F.man 2021; La/idou ct al 2019. Baglioni et al 2021) informed initial studies that showed promise in the removal of overpaint and soiling from gilded surfaces (Sawicki et al 2019. Parts A and B: Ramiro 2021) These gel-like materials were shown to overcome challenges posed by other cleaning systems, by demonstrating:
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PVOH-Borax Cels: Network Modification Ideas
— z
Adding 1% agar, agarose, or gellan ^
• Should be heated with PVOH solution ||
• Adds rigidity °£
• Limits adhesion on cellulosic surfaces 1=
21 o
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Adding gelatin, high percentages (>10%) ~;
• Improves particulate pick-up <s
• Bloom separately; should be added to PVOH solution as it cools
• Creates a double network that resists creep si
Adding cellulose powder: poulticing paste
©
PVOH-Borax Cels: Network Modification Ideas - Agar/ose
a			!H s 111,1 11 ■			
	HP"/					Agarose random _ coils Agarose bundle of ^5™*^ double helices
						
						PVA Chain -
	a		1I1S8			Borax 9
Temperature - 90* C			<1st| TemperMuni - 45* C (2nd) Adding cleaning agents (3rd) Adding the borax		Gelation of the double network hydrogel after cooling down	
Al-Emam, E., Soenen, H., \ Caen, i.etal. * Characterization of polyvinyl alcohol-borax j= /agarose (PVA-B/AG) I double network hydrogel \ utilized for the cleaning ofs works of art. -HeritSci8, 106 (2020). i https://doi.org/10.1186/sj 40494-020-00447-3 -
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PVOH-Borax Gels: Network Modification Ideas - Gelatin
(a)
Gelatin
Water bath heating 50°C
(b)
^ PVA    'V Gelatin Borax
Borax
Mechanical stirring
X
H. Yu, L. Zhao, L. Wang, J. Appl. Polym. Sei. 2023, 140(20), e53852.
https://doi.Org/10.1002/a pp.53852
Omin III PVA/B PVA/G/B	20m im	1
	PVA/B PVA/G/B	
		
60mm
PVA/G/B PVA/B PVA/G/B
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PVOH-Borax Gels: Suggested	1 n T ROD R N  1 C C
Applications	UCTION TO ) ll ECT1E C E
• Surface particulate removal	HYDROI N T RU M K
• Coating removal (solvent additions)	;els i E D E R l
• Work on complex topographies	z ^ o a o — z
• Glue rehydration & removal	_ tn co m 73
• Cleaning plastics and other sensitive surfaces	iTION M 0V E
• Stain removal	cleaning VIBER 2 0 2 4
	O
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NANORESTORE* GELS
141
Nanorestore® Cels: Dry
Nanorestore Gel Dry
• poly(hydroxyethylmethacrylate)/ polyvinyl pyrrolidone) [pHEMA/PVP] semi-interpenetrated chemical hydrogels (i.e. covalently bonded)
• Available: 'Medium Water Retention' & 'High Water Retention' (MWR & HWR)
• Highly retentive - in some applications, safe for water-sensitive surfaces
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Nanorestore* Cels: Dry
Moisture Retention
o °
Table 1 Compositions (w/w) of the selected semi-IPN hydrogels; HEM A/MBA and HEMA/PVP ratios
	H5Q	HS8	H65
HEMA {%)	25.0	16.8	10.5
MBA (%)	0.2	0.2	0.2
PVP (%)	24.9	25.1	24.4
Water (%)	49.9	57.9	64.9
HEM A/MBA ratio	1:1 x 1CT2	1:1.5 x 1CT2	1:2 x 1CT2
HEMA/PVP ratio	5Ü/5Ü	40/60	30/70
The acronym HXX	refers to the	XX percentage of	water in the
Table 2 Some physicochemical properties of the selected p(HEMA)/ PVP, acrylamide [71 and polysaccharide hydrogels
G (%)   EWC (%)   Water release (mg/cm2)
H50 H58 H65
Acrylamide "Hard" Acrylamide "Soft"
90
78 74 95
72 80 87 95 97
reaction mixture
8
15
16
27 56
Agar Art	97	30	
Kelcogel	97	33	
Appl, Phys. A (2014) 114:705-710 DOI 10.1007/S00339-013-8150-0
143
Nanorestore9 Cels: Dry	INTRODUCTIO R N  I COLLECT
Practical Considerations	1 TO    H > IE C E N T F
•EUR 18.00/150cm2 sheet	DROGE ; U M NE
•Very consistent processing	LS IN C t OERLAND
•Clear, somewhat brittle gels	»NSERVA 18-22
•Can be loaded with aqueous solutions, microemulsions,	TlON ( ^ 0 V E I
structured fluids, some polar solvents	: LEAN B E R l
•Possible to clean and re-use	^ a o
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Nanorestore* Cels: Dry
Practical Challenges
•MWR and HWR Dry gels can develop cracks and tears
•Gels become unusable if allowed to dry fully
•Gels can support biological growth; cleaning is difficult
•If loaded with solvent, further use for aqueous delivery is not recommended
o °
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Nanorestore* Cels: Dry Applications
Recommended Applications •Use on "flat" surfaces
•Humidification, surface cleaning, stain reduction
•Controlled delivery on water-sensitive surfaces
•Slow swelling and dewetting of adhesive residues and coatings
•Cracked/porous surfaces where residues are a concern
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Nanorestore* Gels: Dry Applications	
Ml	
	
Ml	\TION CLEANING NOVEMBER 2 0 2 4 E U < E
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Nanorestore* Gels: Peggy
Nanorestore Gel Peggy
• polyvinyl alcohol) and polyvinyl alcohol)/poly(vinyl pyrrolidone) hydrogels
• Available: Peggy 5 [polyvinyl alcohol)] and Peggy 6 [PVA/PVP] as sheets, gums (erasers), and pens
• Flexible, elastic
• Conforms to rough surfaces (Peggy 6 more so than Peggy 5)
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Nanorestore* Gels: Peggy	INTRODUCTI RN  I COLLEl
Practical Considerations	ONTO ) TIECE
•EUR 18.00/150cm2 sheet	HYDR ^ T R U M
•Very consistent processing	OGELS II M E D E RL
•Semi-opaque, flexible, elastic gels	^ o a o — z _ tfi co m
•Can be loaded with aqueous solutions, structured fluids,	RVATII -22 NC
microemulsions, some polar solvents	^ z s o
•Possible to clean and re-use	IANING ER 2 0 2 4
	o
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Nanorestore9 Gels: Peggy
Practical Challenges
•Peggy gels less retentive than Dry; Peggy 6 less retentive than Peggy 5
•Gels become unusable if allowed to dry fully
•Peggy gels can support biological growth readily
•More limited solvent compatibility than Dry gels
•If loaded with solvent, further use for aqueous delivery is not recommended
o °
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Nanorestore* Cels: Peggy
Recommended Applications
•Use on "flat" or rough surfaces. Peggy 6 conforms better to rough surfaces than Peggy 5
•Humidification, surface cleaning, stain reduction
•Controlled delivery on sensitive surfaces; limiting mechanical action
•Cracked/porous surfaces where residues are a concern
•Tape/adhesive removal •Adhesive reactivation
o °
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Hydrogel Solvent Compatibility		INTRODUCTIOI R N  | COLLECT
Because Nanorestore® gels are consistent from batch to		—I 1!
batch, their polar solvent compatibility is known:		f D R 0 G * U M N
Gel Dry	Gel Peqqy	els i E D E R i
Benzyl alcohol	2-Propanol                Xylenes Hydroalcoholic	> z z o
Acetic acid	a                             _ .                           solvents (50%) Acetone                    Toluene                                v '	a o — z _^ <s>
Ethylene glycol	Butyl acetate	■ -J3 to >
2-Methoxyethanol	Cyclohexane	r i o n M 0 V I
Ethanolamine	Ethyl acetate	m m
Propylene glycol	Heptane	73 > r-o Z
Ethanol	Methyl ethyl ketone	^ a
Methanol	1-Pentanol	
2-Butanol	Propylene Carbonate	©
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TJ — z z Hydrogel Solvent Compatibility — Z		
Gel Peqqy Hydroalcoholic solvents (50%)		TO    HYDROGELS IN CONSERVATION CLEANING A ECENTRUM NEDERLAND |  18-22 NOVEMBER 2 0 2 4 W
153
Nanorestore* Cels: Peggy
o °
Bartoletti, A., Barker, R., Chelazzi, D. et al. Reviving WHAAM! a comparative evaluation of cleaning systems for the conservation treatment of Roy Lichtenstein's iconic painting. Herit Sci 8, 9 (2020). https://doi.org/10.1186/s40494-020-0350-2
154
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Nanorestore* Cels: Key Decisions
23
— Z
—11
73 -<
Surface area to be treated (can be cost l\
m m
prohibitive) 1= Improved surface contact (Peggy gels) vs. II improved moisture retention (Dry gels) il
''• z
^ <">
m m
So/vent compatibility I I
Are other gels feasible?
155
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NEW BIOPOLYMER HYDROCEL FORMULATIONS
156
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Synergistic Polymer Interactions	INTRODUCTIO RN  1 COLLECT
Coupled gels	M TO H 1ECENT
• Individual components do not gel on their own	7J ■< cz o m 73
• Interactions between chain backbones, ordering of ionic	o ^ GJ □ m
regions and side chains create physical gels	m (r> TO
• Exact mechanisms are not well understood	^ o a o
• Often: stereochemical similarities between backbones	MSERV, 1 8-22
Synergistic effects:	\TI0N C ^OVEM
• Increased solution viscosity	B E R
• Gel formation	2 0 2 4
• Modification of syneresis behavior	O
157
Example Culinary Gel Synergies	Agar	Carrageenan (iota)	Carrageenan (kappa)	Gelatin	Gellan (low acyl)	Gellan (high acyl)	Guar gum	Konjac	Locust bean gum	Starch	Xanthan
Agar											
Carrageenan (iota)											
Carrageenan (kappa)											
Gelatin											
Gellan (low acyl)											
Gellan (high acyl)											
Guar gum											
Konjac											
Locust bean gum											
Starch											
Xanthan gum											
o
158
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Formulation Inspiration
Contents lists available at Si itnccDiieci
Food Hydrocolloids
journal riomepa^H:        slsav Br.cOrtVlüCaWraüdlH
Increasing xanthan gum content could enhance the performance of agar/ konjac glucomannaji-based system
Dongling Qiao   Wenjuan Shi , Man Luo , Wanting Hu , Yuchun Huang '', Falang Jiang , F«igw«i Xie"'' \ Binjia Zhang11'*
' i:iju n  J' 111... (J. rHV.............: IT frlllH-      JI.H.V7. .l.ir.V.H,
ewwdn*. mha wwrmv r4 rwhnc+w. "liton www, O
''&lw>\ a/tngiwffin& Hauaari* ftewcAsltc upon Fy
} ■ ciwjf r,i-r:,*.i,ir .....j..........nr-ii.i.'..
United States Patent
Milwii el
Patent Number: Date of Patent:
4,S9*,2S0 laa. 16, 1990
[751   InUHiWTS!   G*ry D. Miismc; Colli T. Presc, bath uf Melton MawbEBy. United. Kingdom
Europas Pit Ott
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FOREIGN PATENT ^K.:.. I. v.l.N .-, MM   I/JSB3   EllfOptU Pal Off.
|¥7] ABSTRACT
TheTino-irreversible jquefluj gcis are TJMpired by sub-
jcLt;r.E .i gelliible mmbmlioii «F ™il3wn jTjm and a.
|irc:'L'is.bl> ::ic ...mm   ■! in
AmciplKiptiiilai bpeeks it a pH above 4 to i hm trtu-□KDiikodtrcDiHlitaiis of lemperalnre and lime lo-CEiise the gel to become thenxio incvenlbk. TTit pH LsprcfcT-ibly between 6 ud 10 and more especial] y between i and S. The preferred r»fo of MEthan pun to gliiccnwi-□sn fe in the range of from 5*5 ta 51 5. mare Kpeeinliy l;]HJ to 11:1 and. the preferred concentre lion oTmiiIIuc iunxd glucOmmiiMii in. the wnieSw phise is 0.(0^5 It-&h, inert pref=rabL/fkS to *%, br wKiphl. TncthernW-HTerertWe feU Of 0«r nivEiiLign, ivilb :Ti= induxbn ■ id" f<;«l muLecijil,, suth jk minced mr^t, bvi1 and v*aBLi-MiiujjlL 1'iu !."■ 11." ' i:f :qIl:j. uitj! ..jll'j.s jnil
other food itniciuies.
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Formulation Inspiration
TEXTURE
A hydrocolloid recipe collection
Edited by Martin Lwsöi
jamesdempsey2005
C Q V
jamesdempsey2005 I see straight through you! #sundaythrowback
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Formulation Inspiration
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XANTHAN/KONJAC-ACAR HYDROCELS
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Xanthan Cum
Bacterial branched ionic gum •Cellulose backbone •Anionic trisaccharide side chains
Practical Considerations
•Inexpensive (USD 6.80/1 OOg) Z% •Readily hydrates in cold water c =
''- z
•Typical concentrations: 0.75-1.5% |«
m m
•Very viscous solutions z\
^ z
•Exceptional shear thinning -n • Non-gelling on its own
O
Konjac Clucomannan
Plant polysaccharide
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■uiopyreiioK   p |L —4J    nuMiopaiuiaM   f!(l-*4)   slump yranose   |S (1—d> glLiflipyrai
OH 0\-
-Root vegetable _  U U
•Glucose/mannose backbone •Acyl substitutions
Practical Considerations
•Inexpensive (USD 7.00/100g) •Readily hydrates in cold water •Typical concentrations: 0.75-1.5% •Very viscous solutions •Shear thinning
•Can form a hydrogel by treating with pH 9+ & heating to 90°C
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Xanthan/Konjac Hydrogels: Exceptional Elasticity o —1		
m ° • Prepared in the same methods as agar/ose, creating a strong, H clear, elastic gel 11 m m		
1% Xanthan gum		S I N CO E RLA N D
1% Konjac glucomannan		NSERVATION CLEANING 18-22 NOVEMBER 2 0 2 4
		
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Preparing Xanthan/	I N T ROD R N  | C C
Konjac Hydrogels	UCTION I LL ECT
Recommended: immersion circulator	°o
• Set temperature to maximum.	73 -< cz o
• Prepare a solution of 1 % xanthan and a second solution of 1 %	i G E L ! N E D E
konjac. Stir to combine*	> Z
• Submerge in the water bath, mixing occasionally until internal	a £ — z _^ u>
temperature exceeds 90C.	co rn ^ >
• Carefully remove from bath.	TlON MOVE
• Stir to mix. Pour into mold. Let cool.	C LE A VI B E R
• Rinse to remove unentangled polysaccharide at surface.	MING 2 0 2 4
Microwave method works well, too.	e
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Xanthan/Konjac Hydrogels: Notes
Konjac often has a "fishy" odor depending on its source and purification methods. This odor can be diminished by rinsing or by lowering the pH of the solution.
Xanthan/konjac hydrogels can be pushed to conform to surfaces, and the gel will settle into small surface irregularities.
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Xanthan/Konjac Case Study: Iron-Stained Marble, c. 1500
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Further Modification: Xanthan/Konjac-Agar Hydrogels
1.5% (w/v) total concentration
• Not a gel - viscous fluid Weak gels - poor performance
• Flexible/elastic gel behavior
• Brittle/rigid gel behavior
Region of interest: "new" gel properties
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% Agar
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Further Modification: Xanthan/Konjac-Agar Hydrogels
1.5% (w/v) total concentration
Not a gel - viscous fluid Weak gels - poor performance Flexible/elastic gel behavior
Brittle/rigid gel behavior
Gel adhesion to Whatman filter paper
% Agar
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Further Modification: Xanthan/Konjac-Agar Hydrogels
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1.5% (w/v) total concentration: 2 parts xanthan 2 parts konjac 1 part agar
Blend dry ingredients
SLOW addition to
water with mixing
(or mix separate
solutions)
Heat> 90°C
Cast
O
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Further Modification: Xanthan-Konjac-Agar Hydrogels o				
	of i		* "'^^BHySsH f      :    •', •SSfflP'', .*• *» JBBl	J TO    HYDROGELS IN CONSERVATION CLEANING ECENTRUM NEDERLAND |  18-22 NOVEMBER 2 0 2 4
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Further Modification: Xanthan-Konjac-Agar Hydrogels
In this video:
2% (w/v) total concentration: 2 parts xanthan 2 parts konjac 1 part agar
Estimated cost, including power for stirring and operation of immersion circulator bath (4 hours): $0.87 for 20cm x 25cm x 2mm gel
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Preparation Tips: Xanthan-Konjac-Agar Hydrogels
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Thorough mixing is critical to avoid weak and tough regions
Insufficient heating will result in a grainy, weepy gel
XKA gels are able to be reheated several times without loss of mechanical properties
If the gel isn't good: cut it into pieces and reheat!
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Preparation Tips: Xanthan-Konjac-Agar Hydrogels
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Practical Use:
Xanthan-Konjac-Agar Hydrogels
"Loading" a cleaning solution:
• Initial preparation of the gel
• Soaking a freshly prepared gel
Xanthan-konjac-agar(ose) gels can be dehydrated and stored.
Dehydrated gels can be rehydrated with aqueous cleaning solutions, with minimal change to gel performance.
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Case Study:
CACP1293, Deposition with Angels
Deaccessioned from Harvard Univ. Anecdotes: Used for testing varnishes and cleaning, dating to Gettens and Stout.
AtWUDPAC:
• Microscopy studies
• Cleaning experimentation
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7J ~ Case Study: Deposition with Angels r- o					
	I B Willem		j		IN TO    HYDROGELS IN CONSERVATION CLEANING A TIECENTRUM NEDERLAND |  18-22 NOVEMBER 2024 V
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Case Study: Depositton with Angels
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Residual varnish: slight effect with alcohols and ketones Pigment pickup with other polar solvents Aqueous tests:
• > pH 8: some coating fractions removed
• Significant improvement with chelating agents; DTPA most effective
• Additional improvement with deoxycholic acid
Goal: reduced mechanical action
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Case Study: Chinese Export Lacquer Table
1.25% 2:2:1 XKAgel Prepared with 1 % EDTA, pH 5.0 buffer
Credit: Caroline Shaver
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Nesting
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Case Study: Tenacious Lining Removal
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Case Study: Adhesive Tape Removal
Promising tests! 1.5% 2:2:1 XKA
Ethyl acetate/propylene carbonate/SDS microemulsion 0.5% citric acid, pH 6.5
Long exposure, adhesive dewetting
Credit: Chris Stavroudis, Michelle Sullivan
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Direct Casting
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Must be certain that heating and mixing is adequate.
Poorly heated/mixed/hydrated solution will result in residues!
When direct casting, consider a preparation with a higher agar(ose) ratio: 1:1:1 or 1:1:2?
When heating, do not drive off all of the water, but do not undercook. Do not fail through your own gutlessness.
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Formulation Substitutions:		
	Xanthan/Salep-Agar	JUCTION Tl OLLECTIEC
		3    HYDROGELS IN CONSERVATION CLEANING ENTRUM NEDERLAND |  18-22 NOVEMBER 2 0 2 4
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Formulation Substitutions:
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We can substitute several different h
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glucomannans (konjac, salep, e.g.) P or galactomannans (locust bean gum, tara gum, e.g.) % to produce gels with similar properties! l\
co rn
1 73
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Solvent Additions:
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We can blend non-mjscjble (or low miscibility)
solvents after heating and before gelation. ll
a a m TO
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2% XKA is capable of stabilizing about 15% (w/w): P
• benzyl alcohol is
• ethyl acetate zl
• ethyl lactate l\
• propylene carbonate B
• others si
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Early Mechanical Testing 0 UD	INTRODUCTION RN  1 COLLECT
Early tests:	TO    H YD EC E N T R L
• Yield stress increased with the addition of calcium	m 73 o 21 CI □ m
acetate	1X1 u> 73 > Z
• Gels can be melted and re-gelled several times	21 O a O — z _^ <s>
without loss of mechanical properties	co rn 1 73 *o >
• XKA gels begin to melt around 55C	J 3 A 0 [\ ) NOIJ
• XKA gels can swell 2-3x original size on rehydration	m m 73 > z
• Mold growth visible after 48-60 hours at ambient	o z
conditions with no preservatives	O
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CURDLAN HYDROCELS
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Curdlan HqrXo	Oil ^-O OH	r- CZ i— O o —
OH Bacterial beta-glucan		)N TO 1 T 1 EC E N "
•(1—>3)-P-D-glucose polymer, high MW		iYDROG "RUM NE
Practical Considerations		ELS IN : D E RLA f
•Fairly expensive (USD 25.00/1 OOg)		o a O — z . <s>
•Gels upon heating beyond hydration temperature (heat set) Z%		
•Forms an opaque elastic, retentive gel upon heating above %z		
195°F.		■ z ^ o
•Thermo-irreversible; good temperature stability		EANI I E R 2
•Can form a softer thermo-reversible gel if not heated >150°F		
•Gel structure, flexibility & toughness depend on		
solution concentration and solution heating		©
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Curdlan
Cholesterol Omg	0%l
Sodium 11 Omg	5%
Total Carbohydrate 4g	1%
Dietary Fiber Og	0%
Total Sugars Og	
Includes Og Added Sugars	0% 0%
Not a significant source of vitamin D, calcium, iron, and nntassium	
•The % Daily Value (DV) tells you how much a nutrient serving ol lood contributes to a Oaily diet 2.000 calon day is used for general nulrition advice.	sa
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Ingredients: Water, coconut oil, white rice flour, pea starch, tapioca starch, natural flavors, curdlan gurt^salt. natural smoke flavoring, maple gum acacia, apple extract, beet juice concentrate, purple sweet potato extract, yeast extract, inactive drr yeast, lemon juice concentrate
ried
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Curdlan
Current supplier: MarkNature
iMarkNature
Home     All Collections v      Products v      Sates     Shipping      Informations v      Connect v
Curdlan, High-Performing and Versatile Vegan Thickening Agent
Weight: 1 pound I454g>
I poundI454gt
10 Pound(4540g)
Price: €48,61
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Preparing Curdlan Hydrogels
m
_1_1_^ » >
0        20       40        60       80       100     120 s| Temperature (°C)
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Curdlan Gel Strength: Concentration and Temperature
3 *°o-
2       3 4 Concantrabon (% wW)
Fig. 20.7   Concentration dependence of gel strength for curdlan at 30 °C* (curdlan gel was obtained by heating at 90"C lor 10 min).
50     60     70     80     90 100 Mealing tempera*** fC>
Fig. 20.8   Effect of heating temperature on gel strength of curdlan at a concentration of
3%.:
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Preparing Curdlan Hydrogels
Recommended: hot water bath ^
• Set temperature to 1Q5£E is
• Prepare a curdlan slurry. 5-25% (w/v) in distilled water, ^ in a small plastic zip-top baggie. Shake and manipulate to ^ achieve even dispersion. E"
• Pour a thin layer (~2-3 mm) of the slurry into a flat-bottomed J beaker or jar, or suspend the baggie in the water bath. ~i
• Suspend the container in the water bath for at least 5 minutes,
up to 1 hour. %
Z
• Allow the curdlan gel to cool. Remove from container. p
• Rinse to remove unentangled polysaccharide
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Preparing Curdlan Hydrogels
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Curdlan gels will take on the shape of any form once the dispersion reaches the heat setting temperature.
Ideas:
• blocks
• sheets
• "noodles"
• lozenges/pointed erasers
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Curdlan Gels: Useful Properties	introducti RN  | COLLEC
• Heat setting - additional options for gel preparation	onto h Tl ECENT
• Subsequent temperature stability	ydroge RUM N E[
• Can be warmed/heated	m (r> TO
• Can be frozen!	^ o a o — z _ tfi
• Impressive water retention	ervation 3-22 N0VE
• Very high gel strength & cohesion:	;leanin MBER 20
Good for mechanicaltechniques	
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Comparing Curdlan 8 Peggy Gels
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Time-lapse: 30s, water transfer to KimWipe. 10% Curdlan (left) and Peggy 5 Gum (right), both loaded with the same aqueous solution. o
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TJ — Testing Curdlan with Chelators		
	___!	ON TO    HYDROGELS IN CONSERVATION CLEANING Mk TIECENTRUM NEDERLAND |  18-22 NOVEMBER 2024 W
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Curdlan Hydrogels: Notes
Curdlan gels will promote biological growth after just a few days; limit air exposure
Curdlan gels can be warmed to increase the activity of diffused moisture
Gel strength decreases with increased inorganic salt concentration and/or solvent in initial formulation; recommended to prepare a gel first and then load it with a cleaning solution
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Curdlan Hydrogels: Recommended Uses
Controlled humidification:
• Cast sheets for overall humidification
• "Noodles" for humidifying individual creases
Dampened eraser:
• Cut/cast blocks
Delivery of aqueous cleaning preparations
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Curdlan Hydrogels: Recommended Uses
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SOLVENT COMPATIBILITY
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Hydrogel Solvent Compatibility
Remember that hydrogels are generally 90%+ water by mass, and that the gel structures are often stabilized by hydrogen bonding and the ionic environment.
Changing the solubility parameters of the liquid phase can cause gel instability, densification, and phase separation.
215
Hydrogel Solvent Compatibility
23
— Z
Water-miscible solvents can be tolerated by most hydrogels ^ in small proportions. Solvents with high hydrogen bonding if (alcohols, especially) are expected to be tolerated up to 50% v/v in some cases. ll
a 0
— z
_^ in
co m
1 73
High dipole solvents and solvents with a high dielectric constant (able to separate charges) can cause some gels to tighten and become more dense, %
z
but they may be tolerated at upwards of5-10% mixed into the initial formulation prior to gelation
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Key Properties - Polar Solvents
Solvent	Formula	Density	Water Solubility	Dipole Moment	Dielectric Constant	Viscosity	Notes
		g/mL	g/100g	(D)		mPa»s	
Acetone	C3H60	0.786	M	2.85	21	0.30	
Acetyl acetone	C5H802	0.975	16	3.0	23	0.60	Hazardous material! Interesting ability to act as a chelating agent
Benzyl alcohol	C7H80	1.042	3.5	1.7	13	5.47	
1-butanol	C4H10O	0.81	7.7	1.7	17.5	2.59	
Dimethyl sulfoxide	C2H60S	1.092	M	3.9	46.7	2.00	
Ethanol	CH206	0.789	M	1.7	24	1.08	
Ethyl acetate	C4H802	0.894	8.7	1.78	6.0	0.43	
Ethyl lactate	C5H10O3	1.03	M	3.46	13.1	2.71	
Methyl ethyl ketone	C4H10O	0.805	25.6	2.8	18.6	0.41	
N-methyl-2-pyrolidinone (NMP)	C5H9NO	1.028	M	4.1	33	1.65	
2-propanol	C3H80	0.785	M	1.66	19	2.07	
Propylene carbonate	C4H603	1.205	24	4.9	64	2.47	
Water	H20	0.998	M	1.85	80.1	0.89	
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Hydrogel Solvent Compatibility		INTRODUCTIOI R N  I COLLECT
Because Nanorestore® gels are consistent from batch to		—I 1!
batch, their polar solvent compatibility is known:		ť D R 0 G * U M N
Gel Dry	Gel Peqqy	ELS I E D E R I
Benzyl alcohol	2-Propanol                Xylenes Hydroalcoholic	> z z o
Acetic acid	a™+~„~                    _ .                           solvents (50%) Acetone                    Toluene                                v '	a o — z _^ <s>
Ethylene glycol	Butyl acetate	■ -J3 to >
2-Methoxyethanol	Cyclohexane	r i o N M 0 V I
Ethanolamine	Ethyl acetate	m m
Propylene glycol	Heptane	73 > r-o Z
Ethanol	Methyl ethyl ketone	^ cy
Methanol	1-Pentanol	
2-Butanol	Propylene Carbonate	O
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PVOH-Borax Cels: Useful Solvents
Solvents can be added to PVOH solution prior to mixing
• Ethanol
• Isopropanol
• Methyl ethyl ketone
• Immiscible solvents (benzyl alcohol, e.g.) can be stabilized with a surfactant
Additions of 20-30% (v/v) possible Surfactant additions: 1-2%
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PVOH-Borax Gels: Solvent Effects
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, Valencia 2023
Developing conservation practices for cleaning gilded surfaces: Applications for xPVOH-borax organogels to clean two gilded frames
Variables:
• PVOH MW
• PVOH Wt%
• Borax Wt%
• Gel age
• Solvent(s)
Genevieve Totxn
M Gritorr al New Sou* MWn
Sfdrwy NSW taMl
•ig»! UM *ypt»r, -qa y. lu M ,1 [ g o r .• ,t t ,1 SawiCkl
Keywords pdtfwtyi *cohoJ)-bonu. rJ8psrsjon»(HVPO) 9Wed objects, frames
introduction
Interest in high-viscosity polymeric dispersions (HVPDs) of partially hydrolysed polytvinyl alcohol) borax (xPVOH-b) for cleaning cultural materials K am.Mli et al 2009. Angelova elal 2011.2015. 2016. 2017. and 2018. Angelova 2013. Ricdo el al 2015 and 2017. Duncan 2017. Al-Emam et at 2019 and 2020. Al-F.man 2021; La/idou ct al 2019. Baglioni et al 2021) informed initial studies that showed promise in the removal of overpaint and soiling from gilded surfaces (Sawicki et al 2019. Parts A and B: Ramiro 2021) These gel-like materials were shown to overcome challenges posed by other cleaning systems, by demonstrating:
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Microemutslon Compatibility
Oil-in-water microemulsions may be compatible with hydrogels, particularly if:
• The water phase makes up the vast majority of the mixture
• The microemulsion is thermodynamically stable at the operating temperature
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Hydrogel Solvent Compatibility
For self-prepared hydrogels, testing for solvent compatibility is critical.
Solution formulation, ionic stabilization, polymer : concentration, and other factors determine a solvent's °s compatibility with the gel structure. l\
°Z
''- Z
Qualitative tests: Place a small amount of gel in a I solvent/water mixture. ~=
° z
• Does the gel shrink, swell, or stay the same size?
• Does the gel change opacity?
ill
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TESTING!
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Variables to Test \	Additional factors:	1 N T RODU CI R N  1 C 0 L L E
Properties to tailor •pH	. Time . Mechanical act.on rd&Tnon-aqueous | solvents	ION TO HYDROGE ■CTIECENTRUM NE
•Conductivity		LS IN 1 DE RLA N
•Use of chelating agents		a o — z 1           — w
•Use of surfactants • Viscosity/rheological agents —>■ gels	. Gel type . eel concentration . processing . clearing procedure	1vati0n CLEANING 2 2 NOVEMBER 202
• Reactive additives: enzymes, redox reagents ©		
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General Testing Strategy
1. Determine safe aqueous parameters for original
2. Test for effective solution parameters, targeting the soiling/grime/stain, etc.
3. Determine which gel structure is most beneficial
• How retentive? Cohesive? How rough is the surface? Do you need optical clarity? Etc.
4. Test methods of loading solution/solvent into the selected hydrogel
5. Determine effective dwell time
6. Test appropriate clearance measures
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RESIDUES AND RINSING
o
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Residues
23
— Z
• Increased likelihood of residues: 7
• "Fresh" gels - rinse with distilled water to remove unentangled polysaccharides p
• Lower concentration gels |=
• Softer gels \\
• Cracked, porous surfaces ~tl
• Reduced incidence of residues:
• Tissue barrier but with altered capillary action l\
• Temporary hydrophobization P
• Clear using appropriate rinsing solution* loaded into gel
o
Residues Visualization	INTRODUCTh R N  I C 0 ll EC
•Qualitative examination:	DN TO n T I E C E N T
•UV-induced visible luminescence	7J -< a o m 73 o
• Particularly useful for absorbent surfaces	els IN : D E R l A
•See: Sullivan (2017)	z a a o — z _^ u> co rn 1 73
•Optical microscopy	ro > °z ''- Z ^ o m m 73 > ° z ©
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Practical Considerations: Rinsing/Clearing
Questions to consider:
• How porous is the substrate/structure?
• Are there any sensitivities to moisture to anticipate?
• Does the delivery method work well with the structure and condition of the surface?
• How likely is clearance? Are you willing to leave material behind as part of your treatment?
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Clearing Aqueous Solutions
• Goal 1: prevent precipitation of solubilized constituents
• Goal 2: prevent new solubilization of preserved materials
• Sub-goal: continue/slow down cleaning
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Clearing Aqueous Solutions
"pH-Adjusted Water"
• dilute mixtures of acetic acid and ammonium hydroxide
• both components volatile
• buffered between 3.8-5.6 and 8.3-10.1
• ionic strength determined by concentration
• formulate according to pH used and estimated conductivity of surface
231
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COMPARING GEL TYPES
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Advantages of Material Diversity
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Cohesive Visco-elastic Gel
Cohesive Flexible Physical
Hydrogel
Xanthan-Konjac/Agar
Cohesive Flexible Chemical Hydrogel
Nanorestore Peggv
233
Nanorestore Dry Nanorestore Peggy PVOH-Borax* Curdlan*
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LOW
Nanorestore Peggy PVOH-Borax*
XKA*
Curdlan
Cure
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Gel Strength
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Solvent Compatibility
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MANY	LIMITED	VERY LOW
		Agarose*
Nanorestore Dn		
	H HI	tear* eggy Gellan*
		KA* Curdlan*
		
239
EASY
Nanorestore Dry
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Availability
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MEDIUM
arose'
anorestore Dry norestore Peggy
orax'
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Recommended Uses
	Agar/Agarose	Gellan	Xanthan-Konjac-Agar/ose	Curdlan	Nanorestore®	PVOH-Borax
Water-sensitive	Very high concentration				Dry Gel: Best option!	Very brief exposures
Stain/Tideline Reduction	Very high concentration					
Fragmented Gels/Pastes					Dry Gel possible	
Warm Pours/Sprays			Sprays not recommended			
Mechanical						
Dewetting/ Long exposure						
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©
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73 — ^ Z
— 73
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Q8A and WRAP-UP
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73 — z Z Course Coals I— o	
1.	o ~ Consider alternative modes of
	delivery for humidification and
	cleaning I
2.	Develop a sense for identifying
	useful gel properties |
3.	Describe methods of formulating
	and manipulating hydrogels to
	match desired effects ©
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73 —
	INTRODUCTION TO H RN  1 COLLECTIECENTI
Thank you for your attention.	r'DROGEL RUM NED
Questions? Contact:	S IN CON ERLAND
Matthew Cushman mcushman(5)udel.edu	_^ u> co m ■ tj
m atth e wc u s h m a n(5) wo rc e ste ra rt. o ra	^ > ° Ö
	''• z ^ o m m 73 > ° z ^ CI fin.
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